Reproduction processes are known in which differences in the tackiness of exposed and unexposed areas of a light sensitive layer are used for image production. The images are made visible by application of a suitable toning material, which adheres only in the tacky areas and can be removed from the nontacky areas. Certain of such imaging materials have a special significance in that multiple, successive exposure and toning steps can be performed with the use of different toners on the same light sensitive layer. Such repeatably tonable photosensitive materials are known and are used commercially for producing multicolor images, for running color proof processes, for preparing color filter masks and electronic circuits as well as for the production of fluorescent screens for color picture tubes.
Especially useful imaging materials for the foregoing purposes have been shown to be those containing a 4-(2'-nitrophenyl)-1,4-dihydropyridine compound. Such a material is disclosed in German Pat. No. 3,429,615 (U.S. Pat. No. 4,604,340). This imaging material can also be used for the fluorescent screens of color picture tubes, which have a black matrix in addition to the dots or lines in the fluorescent pattern, that is, in which the interstices among the light emitting sites are filled or coated with a light absorbing material. The black matrix improves the contrast of the image screen and reduces the reflection of ambient light. However, the production of a black matrix, that is, the application of a fourth color on the fluorescent screen, is technically demanding and causes considerable extra expense.
In the currently known processes, the black matrix is produced either in a first process step or as an adjunct to the preparation of the colored image elements. In the latter case, for example, according to statements in U.S. Pat. No. 4,263,385, a light sensitive negatively tonable material is overall exposed after the production of the fluorescent material pattern, to make the remaining areas tacky and is then toned with a black pigment powder.
A major disadvantage of this method is that the diameter of the fluorescent material dots or the width of the fluorescent material lines must be smaller than the openings of the shadow mask. To achieve this, the corresponding image areas are underexposed, so that it is difficult to attain an adequate toned density and therefore, the image reproduction brightness required in the industry. There is also a disadvantage in that the image elements consisting of comparatively large particles of fluorescent material are contaminated by finely divided particles of the black toner. This also leads to a loss of brightness in image reproduction. Furthermore, the accuracy of the image is affected adversely by the thrice repeated insertion of the shadow mask.
These disadvantages can be avoided if the black matrix material is applied prior to the production of the fluorescent pattern. However, this type of process requires the use of two light sensitive layers. For example, German Pat. No. 3,540,796 (U.S. Pat. No. 4,698,293) discloses a process in which the black matrix is produced on a first negative-working light sensitive layer by image reversal. Then a second negative-working light sensitive layer must be applied on this layer to make the fluorescent material mask.
Another process has been developed in which the matrix pattern can be exposed first with offset lamp positions and then toned. Aside from this process being useful only for the production of fluorescent screens with line image pattern, both methods require complicated, additional process steps.
The problem to which the present invention is directed is that of providing a photosensitive composition for the production of repeatedly tonable layers in the manufacture of fluorescent screens with a black matrix for color picture tubes, which composition makes it possible to produce on a single light sensitive layer first the black matrix and then the fluorescent material pattern for all types of screens.